DOF vs diffraction: If I have this wrong please put me right. Small sensor cameras give better DOF, but suffer more diffraction than a large sensor camera at the same F stop. large...

steve7cat Loc: Swindon uk

If I have this wrong please put me right.
Small sensor cameras give better DOF, but suffer more diffraction than a large sensor camera at the same F stop.
large sensor cameras give less DOF at the same F stop but a higher F stop can be used before diffraction becomes an issue.
So for macro photography is there an ideal sensor size to maximize the DOF
thanks
Steve

Nikonian72 Loc: Chico CA

"Circular aperture diffraction", aka "small aperture diffraction", is a phenomenon of the relative size of an aperture in a lens, having nothing to do with the camera sensor or film. Read more here:
FAQ: Why are my Digital Images Sharper at f/8 than f/22?
http://www.uglyhedgehog.com/t-59819-1.html

Depth of Field is also a phenomenon of the relative size of an aperture in a lens, again, having nothing to do with the camera sensor or film. Read more here:
FAQ: Understanding Depth of Field
http://www.uglyhedgehog.com/t-45532-1.html

dar_clicks Loc: Utah

I have wondered the same thing as the question posed in the original post and for me, while the basics are clear enough, there are still many of the finer points of diffraction that seem counterintuitive (I'll keep studying). The posts and links on UHH seem correct to me, but there is a web page (link below) that does describe the relationship of the photographic medium (film or sensor) to another factor called diffraction limit -- makes for interesting reading and even more to absorb.
http://photo.stackexchange.com/questions/8304/what-is-a-diffraction-limit

In looking for a practical way to accomplish maximizing DOF, there have been other methods described on this site and others that take the final results beyond the limits of the camera and lens itself (focus stacking, etc.). In future I hope to learn some of them.

Nikonian72 Loc: Chico CA

dar_clicks wrote:

. . . there is a web page that does describe the relationship of the photographic medium (film or sensor) to another factor called diffraction limit . . .

Your cited web-article is absolutely correct. It states that circular aperture diffraction is strictly a phenomenon of lens aperture, and that diffraction limitation is a phenomenon of the recording medium, whether digital sensor or film. Diffraction limitation is more of an engineering design problem rather than a photography problem, as there is absolutely nothing we photographers can do about it.

LoneRangeFinder Loc: Left field

Nikonian72 wrote:

quote=dar_clicks . . . there is a web page that d... (show quote)

Except bitch and moan about those darn "airy disks".

Nikonian72 Loc: Chico CA

LoneRangeFinder wrote:

Nikonian72 wrote:

. . . there is absolutely nothing we photographers can do about it.

Except bitch and moan about those darn "airy disks".

Been there, done that.

Croce Loc: Earth

Nikonian72 wrote:

"Circular aperture diffraction", aka &qu... (show quote)

Don't mean to be argumentative Douglas but this seems to contravene your statement that DOF has nothing to do with sensor size. Your statement and the input required on the calculator in the link below contradict each other. What say ye?

http://www.dofmaster.com/dofjs.html :? :? :?:

dar_clicks Loc: Utah

Nikonian72 wrote:

quote=dar_clicks . . . there is a web page that d... (show quote)

A succinct and clarifying response. Thanks.

steve7cat Loc: Swindon uk

Thank you for your reply I followed the links you gave. It seems quite complex, but within the text it says. quote

As two examples, the Canon EOS 20D begins to show diffraction at around f/11, whereas the Canon PowerShot G6 begins to show its effects at only about f/5.6. On the other hand, the Canon G6 does not require apertures as small as the 20D in order to achieve the same depth of field (due to its much smaller sensor size).

my understanding was a point and shoot had better dof than a dslr
Steve

Nikonian72 Loc: Chico CA

Croce wrote:

Don't mean to be argumentative Douglas but this seems to contravene your statement that DOF has nothing to do with sensor size. Your statement and the input required on the calculator in the link below contradict each other. What say ye? http://www.dofmaster.com/dofjs.html

Let us assume that we have built a camera large enough to walk inside. We attach a specific lens, and set to f/4 aperture. We have different size sensors, each mounted to separate stands. We start with the smallest sensor, positioning it inside of camera to capture a specific Field-of-View, focus and capture an image. We then select the next size sensor, move it back slightly, until the same FoV is obtained, then refocus and capture a new image. We progress to the next largest sensor, and repeat. The aperture never changes, the lens focal length never changes, and the Working Distance never changes, hence the DoF never changes. The several images printed to the same size photo paper will look extremely similar, even though they are from different size sensors.

Croce Loc: Earth

Nikonian72 wrote:

quote=Croce Don't mean to be argumentative Dougla... (show quote)

Doug, where can I find one of those cameras? I would like to try that out.
:mrgreen:

All kidding aside, then why do they differentiate between different bodies and sensor sizes in the calculators. They lay it on differing "circle of confusion" factors for the various sensor sizes. For instance taking this set of circumstances: 50mm lens, f/11, subject 10' away. Here is the return data for a 5D MkII full frame body and sensor: Hyperfocal distance 24.3'. Depth of Field near Limit 7.11' far limit 16.9'. For a 7D .6 crop sensor the return data is: 38.3' Hyperfocal distance. Depth of Field near limit 7.95' and 13.5' far limit. The only thing which can account for the difference is that the Full Frame sensor has a circle of confusion of .030mm and the .6 crop sensor has a circle of confusion of .019mm. Now then I would like it known that my circle of confusion is Zero. :? Even though I cannot explain the phenomena. What say ye about this these data differences under equal circumstances except for the sensors?

Nikonian72 Loc: Chico CA

Croce wrote:

Doug, where can I find one of those cameras? I would like to try that out.

They are called Camera Obsuras:
http://en.wikipedia.org/wiki/File:CameraObscura.JPG
http://en.wikipedia.org/wiki/File:CameraObscuraSanFranciscoCliffHouse.jpg
http://en.wikipedia.org/wiki/File:Camera_Obscura.JPG
http://en.wikipedia.org/wiki/File:Camera_obscura_Prague.jpg
http://en.wikipedia.org/wiki/File:Camera_obscura2.jpg

Croce Loc: Earth

Nikonian72 wrote:

Croce wrote:

Doug, where can I find one of those cameras? I would like to try that out.

They are called Camera Obsuras:
http://en.wikipedia.org/wiki/File:CameraObscura.JPG
http://en.wikipedia.org/wiki/File:CameraObscuraSanFranciscoCliffHouse.jpg
http://en.wikipedia.org/wiki/File:Camera_Obscura.JPG
http://en.wikipedia.org/wiki/File:Camera_obscura_Prague.jpg
http://en.wikipedia.org/wiki/File:Camera_obscura2.jpg

Actually I was in that one in SF about 4 years back. It is pretty neat. What do you think about the other part of my comments Doug. The part about the circle of confusion difference of different sensors and the effect on HFD and field of focus etc.??

Nikonian72 Loc: Chico CA

Croce wrote:

Actually I was in that one in SF about 4 years back. It is pretty neat. What do you think about the other part of my comments Doug. The part about the circle of confusion difference of different sensors and the effect on HFD and field of focus etc.??

You are looking for an argument, and I am not interested. Otherwise, you would have previously admitted that you had personal experience with a camera obscura. The phenomenon you question was mentioned above, and you can educate yourself here: http://photo.stackexchange.com/questions/8304/what-is-a-diffraction-limit

Croce Loc: Earth

Nikonian72 wrote:

quote=Croce Actually I was in that one in SF abou... (show quote)

Hey Doug don't get all strung out over nothing. Surely you could tell I was kidding in the first line about where to find one of those cameras. I do not follow your example of the CO. Actually I do not see a similarity in circumstances. You are the one who said sensor size has nothing to do with it. I am not looking for an argument. If you do not know the answer just say so. The calculator says it does have something to do with it and I was asking how you address that matter. If you do not have an answer just say so and I will go away.

PS: I just read the diffraction discussion. It seems to be a different issue. I take it from that article that diffraction more or less affects the entire image. DOF on the other hand does not but rather renders in / out of focus areas on a near / far plane. I think they are 2 different phenomena.